The digital era has given camera buyers abundant new choices. But changes that came with higher-end models called digital SLRs have also imposed new lens complexities and compatibility issues buyers hadn't bargained for.

On the one hand, the engineers behind single-lens reflex cameras, now unleashed from the constraints of 35mm film, can match the image sensors at the heart of digital SLRs to different cost and engineering priorities. On the other hand, because the size of those sensors therefore varies, the same type of lens often produces different results when comparing one digital SLR to another--or to 35mm film SLRs. In one situation, lenses are not just different, but actually incompatible as well.

Consumers, who have shown a strong appetite for digital SLRs and the cameras' accompanying high-quality images, are grasping the new rules. But no one denies there's a learning curve to demystify the details.

Take the case of Jesse Warren, an English teacher and avid photo hobbyist in Shenzhen, China. He concluded that, with lens compatibility issues in mind, he'd be wise to avoid Canon EF-S lenses that work only on small-sensor SLRs and to stick to the EF models that follow the older standard.

"After asking around for a few weeks, I came to fully understand the details of lens focal length and compatibility," he said. "I am very concerned, which is why I will probably invest in EF lenses."

Manufacturers are unrepentant about the newly fluid situation. "Standards always lead to something that makes life easier for the consumers, but it also limits creativity" for camera designers, said Darin Pepple, marketing manager for Fujifilm. "You have to weigh both sides."

On traditional film SLR cameras, a lens with a 50mm focal length closely approximates the optics of a human eye. But smaller sensors on most digital SLRs mean that a 50mm lens has a narrower field of view, which leads to light from a smaller angle hitting the sensor (). As a result, for example, the image of a car that shows completely on a 35mm film SLR might be missing the bumpers when viewed with a digital SLR using the same lens.

A conversion factor is used to describe new-era cameras in old-era terms.

For example, on a Nikon or Fujifilm, a 50mm lens shows the same field of view as a 75mm lens on a film SLR and therefore has a 1.5x conversion factor. On an Olympus or Panasonic, a 50mm lens works like an old-school 100mm lens. And for digital SLR market leader Canon, the equivalent is 80mm for consumer models, 65mm for its midrange line and an unchanged 50mm for top-of-the-line models with "full-frame" sensors.

The issue isn't likely to fluster experienced photographers. But now that digital SLRs cost less than $650--not much more than high-end point-and-shoot cameras--a new generation of less sophisticated buyers is arriving in the market.

Electronics manufacturing issues triggered the change. Although full-frame sensors preserve compatibility with film SLR cameras and produce cleaner images, they're more expensive and consume more battery power. Canon must make full-frame sensors by joining several smaller ones.

"You definitely have an entirely disruptive situation as the silicon guys drive the technology," said analyst Jeff Clark of Current Analysis.

Even as computing technology remakes the camera business and film becomes a relic, the film frame standard endures as a reference point to compare photographic equipment. The 35mm camera standard prevails for describing the lenses even of simple point-and-shoot cameras that lack interchangeable lenses.

New wrinkles for old standard
For decades, photography fans preferred 35mm film SLR cameras for their balance of size, image quality, film cost and the attraction of interchangeable lenses. By attaching different lenses to the same camera, people can photograph everything from wide crowd pictures to distant birds. Enthusiasts and professionals accumulated lens collections to span the range and fit special circumstances.

The 35mm label derives from the size of the film, 35mm wide with a negative measuring 36mm by 24mm. SLR refers to a reflex mirror that reflects light from the lens directly into the viewfinder, then snaps out of the way to expose the film. The design means the photographer sees the same image that appears on the image sensor, even when employing different lenses.

The narrower field of view on many digital SLRs boosts telephoto lenses, those with long focal lengths. For example, a 200mm lens on a film SLR works like a 300mm lens on a Nikon digital SLR or a 320mm lens on a consumer-level Canon competitor.

"The 1.6x factor on the focal length has, for my main subject of railways, been a bonus," said Chris Millner, an English photo buff and deputy editor of The Railway Magazine.

But for wide-angle lenses, a narrower field of view is undesirable. "The one area where the focal length multiplier is a real problem is in the area of wide-angle lenses, said InfoTrends analyst Ed Lee. "To get to a 28mm focal length you will need an 18mm lens, thus forcing some people to buy a new lens."

To make small-frame cameras useful, market leaders Canon and Nikon now concentrate on new wide-angle lenses for digital SLRs, such as Nikon's 12-24mm zoom lens and Canon's 10-22mm competitor.

Adjusting lenses

A standard 50mm lens on most digital SLRs gives a much narrower field of view than on film SLRs. Here are the conversion factors to calculate equivalent focal length.

The conversion issue hasn't been a big problem for Canon because digital SLRs appeal chiefly to experienced buyers, said Chuck Westfall, director of media and customer relationships for the company. "People well understand what they're getting into before they plunk down their money," he said.

That view is reinforced by retired British fireman Chris Brooker, a member of the Harpenden Photographic Society whose activities include taking photos for the Wheathampstead Dramatic Society.

"The 1.6 crop factor seems straightforward," he said. The only controversy he sees is whether 85mm is still the ideal focal length for portrait photography. (Yes it is, he argues convincingly.)

Millner plans to upgrade to a full-frame digital SLR now that Canon released the relatively affordable--though still $3,000--EOS 5D. But it's not a problem that Canon's digital SLR-specific ES-S lenses don't work on the EF-only 5D. "I'm not worried, as I have never bought EF-S lenses," he said.

Canon's lower-end digital SLRs aren't a technological dead end, either. Those cameras' smaller sensor size, called APS-C, "is clearly here to stay," Westfall said. "Because of the cost factors, that's going to be the sensor we end up concentrating on for the entry-level cameras for the foreseeable future." And Canon has begun bringing exotic, high-quality lens elements to its EF-S lenses, though not the weatherproofing of its high-end "L" series of EF lenses.

Canon's EOS 1D Mark II N uses yet a third standard, an intermediate-size sensor with a 1.3x conversion factor to balance processing speed with image quality. "We'd like to continue using that size as well," Westfall said.

Unlike Canon, Nikon has moved to a single "DX" sensor size for its digital SLRs.

"One thing Nikon designers have been very consistent in is maintaining a constant size of our DX sensors," said Steven Heiner, senior technical representative for marketing at Nikon. The sensor size provides good image quality even with its higher-end 10.2-megapixel D200 and 12.4-megapixel D2X, he said.

Olympus, which is hoping the digital revolution will help it reclaim prominence in the SLR camera business, isn't worrying about compatibility between its old-style OM lenses and new models using its "4/3" system. (The 4/3 label refers to the squarer proportions of the image sensor; by comparison, 35mm film frames have a wider proportion of 3 to 2 instead of 4 to 3.)

"We decided to go ground-up digital," said John Knaur, senior marketing manager for digital SLRs at Olympus Imaging America. "In the film camera market, we weren't a major player toward the end of our career. We didn't have a warehouse full of film camera lenses. That allowed us to look at the requirements for digital photography and take a much bolder step than a lot of our competitors did."

"We don't know what the future holds for image sensor changes. But the platform has been built so that, going forward, there is compatibility with anything in the 4/3 system," said Richard Campbell, director of imaging for Panasonic.

Even for those who can't afford to alienate existing customers, redesigning lenses for digital SLRs has opened up new options.

"We're able to create lenses that could not exist for 35mm. Their size, weight and cost would be so prohibitive that we wouldn't sell any," Heiner said. "We once upon a time had a 13mm lens for 35mm systems. It weighed three times as much as the camera and cost as much as a car."

As buyers adjust to the conversion factors, new technology could lead to a resurgence of the older standards, Lee said. "I expect that in the future, full-frame sensors will become more affordable and therefore more popular and will make their way into less expensive consumer digital SLRs," he predicted.

Either way, Canon is unruffled by fluid digital SLR standards.

"The bottom line is what you see in sales," Westfall said. "It's the fastest-growing category in the entire digital-camera market."